Perhaps the most underreported and deadliest aspect of the three explosions and numerous fires to hit the stricken Fukushima nuclear reactor since Saturday is the fact that highly radioactive spent fuel rods which are stored outside of the active nuclear rod containment facility are likely to have been massively compromised by the blasts, an elevation in the crisis that would represent “Chernobyl on steroids,” according to nuclear engineer Arnie Gundersen.

As you can see from the NPR graphic below, the spent fuel rods are stored outside of the active nuclear rod containment casing and close to the roof of the reactor complex. Video from Saturday’s explosion and subsequent images clearly indicate that the spent fuel rods at Fukushima unit number one could easily have been compromised by the blast.

According to Arnie Gundersen, a nuclear engineer at Fairewinds Associates and a member of the public oversight panel for the Vermont Yankee nuclear plant, which is identical to the Fukushima Daiichi unit 1, the failure to maintain pools of water that keep the 20 years worth of spent fuel rods cool could cause “catastrophic fires” and turn the crisis into “Chernobyl on steroids.”

The BBC is now reporting that “spent fuel rods in reactors five and six are also now believed to be heating up,” with a new fire at reactor 4, where more spent rods are stored, causing smoke to pour from the facility.

“Japanese news agency Kyodo reports that the storage pool in reactor four – where the spent fuel rods are kept – may be boiling. Tepco says readings are showing high levels of radiation in the building, so it is inaccessible,” adds the report.

“At the 40-year-old Fukushima Daiichi unit 1, where an explosion Saturday destroyed a building housing the reactor, the spent fuel pool, in accordance with General Electric’s design, is placed above the reactor. Tokyo Electric said it was trying to figure out how to maintain water levels in the pools, indicating that the normal safety systems there had failed, too. Failure to keep adequate water levels in a pool would lead to a catastrophic fire, said nuclear experts, some of whom think that unit 1’s pool may now be outside,” reports the Washington Post[2].

The rods must be kept cool because otherwise they start to burn and, in the case of reactor number 3, would release plutonium and uranium in the form of vapor into the atmosphere.

“That’s bad news, because plutonium scattered into the atmosphere is even more dangerous that the combustion products of rods without plutonium,” writes Kirk James Murphy[3].

“We’d be lucky if we only had to worry about the spent fuel rods from a single holding pool. We’re not that lucky. The Fukushima Daiichi plant has seven pools for spent fuel rods. Six of these are (or were) located at the top of six reactor buildings. One “common pool” is at ground level in a separate building. Each “reactor top” pool holds 3450 fuel rod assemblies. The common pool holds 6291 fuel rod assemblies. [The common pool has windows on one wall which were almost certainly destroyed by the tsunami.] Each assembly holds sixty-three fuel rods. This means the Fukushima Daiichi plant may contain over 600,000 spent fuel rods.”

There have been massive design issues with the Mark 1 nuclear reactor stretching back three decades.

As ABC News reports today[4], “Thirty-five years ago, Dale G. Bridenbaugh and two of his colleagues at General Electric resigned from their jobs after becoming increasingly convinced that the nuclear reactor design they were reviewing — the Mark 1 — was so flawed it could lead to a devastating accident.”

“The problems we identified in 1975 were that, in doing the design of the containment, they did not take into account the dynamic loads that could be experienced with a loss of coolant,” Bridenbaugh told ABC News in an interview. “The impact loads the containment would receive by this very rapid release of energy could tear the containment apart and create an uncontrolled release.”